When considering the structure of the foot as a whole, it is helpful to compare it to a twisted plate (Fig. 16-24); the calcaneus, at one end, is positioned vertically when contacting the ground, whereas the metatarsal heads are positioned horizontally when making contact with a flat surface. Thus, in the normal standing position on a flat, level surface, the metatarsal heads are twisted 90°with respect to the calcaneus.